PLANETARY VIEWING ?? -aperature rules?or telescope type?

[robz (Robert)]

O.K guys, for as long as I can remember, I have allways wanted to be able to visually examine details in planets : the intricate structure of the belts and ovals on Jupiter and variations in the rings of Saturn.........bla, bla, bla,............you know what I mean

I am fully aware that seeing conditions play a big part in this particular field and know that some scopes need to be perfectly collimated/cooled down etc. to stand a chance at revealing any of the fine details I'm after.
I am also aware that what one sees through the eyepeice is not necessarily the same as what is captured and stacked with expensive astro cams and software.

After my last humorous and light hearted post, I thought I might ask for some honest opinions from those who have owned the many various scopes available to the amateur astrononer and are aware of the different performance levels and the reality of what to expect

The questions are as such :

does aperature still rule in revealing planetary details

How does a 12 inch SCT compare against a 12 inch or even a 16 inch dob at the same magnification Does the dob/newtonian need spectacular optics to begin to approach the SCT

Will a 4-5 inch good/medium quality(and price) APO or ED refractor cream all the above at the same magnification

Last of all, are high quality, small aperature(compared to the sizes mentioned above) refractors the ''ultimate'' for planetary viewing or is this just wishful thinking

Love to hear your thoughts

Rob.

[TrevorW]

From memory although not into planetary viewing myself, long focal length (preferably) larger aperture APO refractors have always been considered the pinnacle for this type of observing

[rmcconachy]

G'day Rob,

I suggest having a look at this thread <http://www.iceinspace.com.au/forum/s...ad.php?t=66769> and this thread <http://www.iceinspace.com.au/forum/s...ad.php?t=60382> for some more posts on this topic. I think that inch for inch a Newt is better than a SCT for planetary viewing (less optical surfaces to get right and easier to cool). However, a SCT will be easier to mount on a tracking mount than a Newt. Inch for inch a good refractor will be better still than the Newt but APO refractors get expensive quickly around the 5" aperture range and you can buy a much bigger and cheaper Newt that will perform better for less dollars.

In a nutshell I'd say that yes, good quality well-cooled aperture rules.

[Alchemy (Clive)]

The Newtonian will give you about the best bang for your buck, a 5 inch apo will cost you moderate amounts, I have a FLT 132 you're looking at 5 k plus unless the dollar goes gangbusters. For much less money you could get 16 inches of truss tube dob. Which will definitely give you better views at the eyepiece, as with all things there are scopes and scopes, you could buy a 16 inch meade for around 3k if you want a custom made SDM with superior optics and focuser etc it will cost you more.
You'd have to be able to pick up a 12 inch gso for around 1 k , if you get the bug then you can save for the scope younwill use for a lifetime.
Refractorsare great for imaging and inch for inch they are superior, but you won't find too many apo scopes above 6 inches around.
Then once you have the scope, there's eyepieces to think about, I'd be happy to have a box of televue eyepieces and no other brand, but thats just my thoughts.

[jjjnettie (Jeanette)]

A 10" Dob will do the job. You'll also need a good quality apo barlow and a nice high power eyepiece and you'll be more than happy.
With a little practice, you can even do some basic planetary imaging.

[robz (Robert)]

Thanks for your input guys and gals!

I'll check out the thread links and will probably go and build or buy a large Newtonian for my EQ6PRO mount

[Alchemy (Clive)]

Originally Posted by robz

Thanks for your input guys and gals!

I'll check out the thread links and will probably go and build or buy a large Newtonian for my EQ6PRO mount

Don't forget to buy a stepladder then

[Waxing_Gibbous (Peter)]

I have an 8" Newt and a 4.5" refractor. The refractor shows greater contrast and a 'crisper image', while the newt shows more detail but with less contrast and a slightly softer image. It can do your head in trying to work out the trade-offs!!
Personally I prefer the refractor, but as noted, a good one gets expensive very quickly.
If you are in the position to get one, one of the 'Intes-Micro'
x15 series of Maksutov Cassegrains are reputededly excellent for planetary viewing, without giving a lot away for deep sky.
They have a small (c.25%) central obstruction and an f15 focal length. The 6 & 7 inch seem reasonably priced for what they offer.
Have a boo at tetontelecopes.com for more info.
I have no connection with either company. Its just what I've garnered from reviews and gossip.
Peter

[gregbradley]

I think one way to look at it is what type of scope are the very best planetary imagers using to capture their images?

Mostly they use Celestron SCTs - 9.25, 11 or 14 inch.

Bird uses his own made Newt.

Newts with that much aperture may be hard to handle physically.

The best views I have had was with a Celestron 11 inch SCT.

Refractors give you a sharper view but much smaller image unless barlowed to hell.

I have and have had many fine refractors. I remember a nice view of Jupiter under excellent seeing at my dark site with an FS152. But smallish evne is sharp and stable. The SCT has long focal length for its compact size.

My opinion would be to get a decent view of planets with an APO you'd need more than 4.5 inches of aperture. A 4 inch APO is a rather dim view unless you are looking at wide star fields. A 6 inch APO gives a similar brightness to around an 8 inch SCT as a guideline. It can at times appear brighter because APOs typically have such great contrast and have a very engaging sharp view.


Greg.

[astro744]

Originally Posted by robz

Thanks for your input guys and gals!

I'll check out the thread links and will probably go and build or buy a large Newtonian for my EQ6PRO mount

A Newtonian with a first class mirror is hard to beat on planets if the secondary is kept small, say under 20% obstruction by diameter. To ensure you do get a first class mirror I would recommend you have one made to your specifications than going with a mass produced mirror. It will cost a lot more and it will come down to how good an image you want and how much you want to pay for it. Note a first class mirror will perform on all objects not just planets. Stars will be tighter and fainter fuzzies will be seen.

A large Newtonian will take longer to cool but once stabilised it will out perform any smaller refractor for detail. However, for quick but quality views a small 4" APO is hard to beat. You will see all what the refractor is cabable of showing within minutes of setting up provided the seeing is good of course and this view often rivals larger 'scopes since those 'scopes are still stabilising or optics are mediocre.

Note too a large Newtonian on an equatorial mount really needs a set of rotating rings to ease access to the eyepieces and avoid difficult viewing angles.

[robz (Robert)]

Well, now it's becoming clear thanks to some honest input

Yes, I was thinking of a mass produced mirror for a Newtonian but knew at the back of my mind that it would most likely be of average optical quality.

I'm familiar with refractors(only achromats) and know that they can at times, even though they are not perfectly colour corrected, blow away a newt with much, much larger aperature.
I would not however spend thousands on a 5 inch overpriced APO..........this is just a rip off despite the makers claims on how costly the glass is.

I have a 60mm old tasco(yes,........60mm........with an obviously and unusually good objective) that shows the moons of jupiter as small dots at high power(dare I say disks?!) compared to my 15 year old 8 inch U.K made Orion ( excelent optics) ...........which no matter how well collimated, does not cut the mustard on planets and refuses to show more detail as the aperature should ????????.......the moons look like spiky stars

I would love to own a SCT, but will not bother with anything under 10 inches in the aperature department.

Looks like a lot of money will be needed to get there by the sounds of it.

I guess you get what you pay for

Rob.

[Satchmo]

Originally Posted by gregbradley

I think one way to look at it is what type of scope are the very best planetary imagers using to capture their images?

Mostly they use Celestron SCTs - 9.25, 11 or 14 inch.

I've always found SCT's poor visually on the planets- partly due to the typically 40% obstruction when you take in to account the secondary baffle tube. For planetary photography however it is not so much a problem because image processing and stacking is so good at rendering contrasty images from more tenuous data. The eye of course can't do this in real time , so for visual observing of the planets I 'd recommend a good Newt with clean well collimated optics and less than 20% obstruction.

[robz (Robert)]

Originally Posted by Satchmo

I've always found SCT's poor visually on the planets- partly due to the typically 40% obstruction when you take in to account the secondary baffle tube. For planetary photography however it is not so much a problem because image processing and stacking is so good at rendering contrasty images from more tenuous data. The eye of course can't do this in real time , so for visual observing of the planets I 'd recommend a good Newt with clean well collimated optics and less than 20% obstruction.

Hmmmmm?.....that's interesting Mark, and I have heard this from time to time.

Does anyone know what the BINTEL mirrors for newtonians are like?
I know we're back to mass produced optics here again, but the specs are quite impressive (if true) : surface accuracy at least 1/16 wave RMS (typically better)BK7 substrate.

It all sounds better than your average plate glass slab of Chinese junk does it not?

[Sylvain (Jon)]

Hi,

For planetary viewing, aperture rules.
As long as we are comparing equipments of equivalent optical quality. There is no point comparing an apo to a dob since the apo has excellent optical quality and the dob average optical quality.

For a given night (= at a given seeing) there is a max useful magnification no matter the instrument type.
On a turbulent night, all instruments type perform the same (same maximum useful magnification). Smaller instruments might display an aesthetically more pleasant image due to the smaller aperture "seeing" less turbulences. A bigger instrument can be reduced in aperture to match the smaller one and will deliver the same images.

Under good seeing conditions, a small instrument in aperture might be limited by its resolution (below the maximum useful magnification on that night) whereas a larger instrument will not be.

A second parameter to consider is brightness and contrast. No matter the seeing conditions on a given day, a larger instrument will obviously deliver brighter images, which in turn helps seeing details of low contrast.
Consider the following images:

http://www.astrosurf.com/altaz/images/image020.jpg

Obviously, the details are easier to figure out in the brighter images.
This is why, for planetary observations, aperture (and optical quality) always rules.

[The Mekon (John Briggs)]

The only times I have seen planetary images as good (and better) as in my 130mm Apo is through longer focus high quality Newtonians, (10" F6, 8" F7) At these times the Newts had had plenty of time to settle in temperature and the seeing was excellent.

In average conditions and straight out the box, the refractor blows all comers away.

Also I have never seen a 8" SCT that could better the 130 on any object, deep sky or otherwise.

[robz (Robert)]

After reading forum member's rmcconachy's links (especially ''Damian Peach's VIEWS OF THE SOLAR SYSTEM'') there is no longer any question in my mind what I will settle on for planetary viewing and photography at a later stage.

It is clear that aperature is superior and that the B.S. spread on the central obstruction is not the'' image/contrast killer'' it's made out to be

As a Newtonian of ''adequate aperature'' (12 inch or more)no matter how implemented, will be a long, cumbersome beast and PITA to keep in collimation, I'm will go for the latest 12 inch Meade LX200 - ACF SCT OTA on my EQ6PRO Mount.

I know it has excellent optics with minimized aberations and combines the benefits of many other optical systems. No,.......it's not the perfect scope and has it's drawbacks, but more SCT'S are sold world wide as the main telescope system in multiple scope set ups and are the choice of many small semi professional observatories.............and rightfully so....!

[rmcconachy]

If you are just interested in planetary rather than wide field viewing then a normal SCT should be just as good optically as a Meade ACF or Celestron EdgeHD scope. Planets are small and the optical changes in both relative to a normal SCT are about improving the off axis views rather than the on axis views (although the EdgeHD is now better ventilated than the older Celestron SCTs I believe).

If you want to go into imaging, focus (bad pun) on obtaining a big steady mount with smooth periodic error. Talk to bird, gregbradley, strongmanmike and the other great imagers who frequent this place for recommendations.

Lastly, the links I posted in my previous message weren't mine, all of the good stuff came from other people. Kudos and thanks to them!

[AstroJunk (Jonathan)]

Robert, the 12" SCT will do very nicely for lunar an planetary work. I have the 14" and it has very nice optics for the price.

If you really want to sell your soul, try a Takahashi Mewlon with which you can get the trifecta of aperture, quality and minimal central obstruction.

[Sylvain (Jon)]

rmcconachy is correct: the EdgeHD & equivalents are SCT with a built-in field flattener. Therefore they are not going to perform better than regular SCT when paired with tracking mounts.

There is no magic. All optical instruments obey the rules of physics. APOs included. They however are terrific instruments, in their aperture class.

[Sylvain (Jon)]

Yep, mewlons are said to be very nice, but apparently require fine tuning to deliver their best.